Earth bonding in a TT system

[Anydm]

Hi
I have just purchased a house with a TT supply. The last EICR was carried out in 2021 with no C1 or C2 failures. The CU is up to date with a full complement of RCBOs for all circuits together with a SPD. The main earth is provided by a buried rod on the other side of the wall outside the house connected to the consumer Earth terminal. This in turn is bonded to the gas supply sited next to the electricity meter and CU. However… there is no earth bond to the incoming waiter supply (sited at the other end of the property). The central heating combi boiler located in a room on the first floor does have all incoming and outgoing copper pipe work cross-bonded (although I didn’t think this was any longer necessary). In the relevant box in Section 12 of the 2021 EICR (Bonding of extraneous conductive parts to water installation pipes) the inspector has simply marked ‘N/A’. Does this seem appropriate or acceptable?

 

[DetlefSchmitz]

I would say that n/a would only be valid if the incoming water pipe is plastic.

 

[Murdochcat]

I would say that the incoming water pipe should be bonded

 

[jurassic sparkk]

I would say that the incoming water pipe should be bonded

Cannot say without testing if that 'pipe' is an extraneous conductive part.

 

[Murdochcat]

Cannot say without testing if that 'pipe' is an extraneous conductive part.

I did say “should”

 

[JohnW2]

I did say “should”

"should" means something like "ought to be", doesn't it?

If the outdoor part of the water supply pipe were plastic (hence not an extraneous-c-p") it surely would not "ought to be bonded"? As was said, we can't tell whether it needs bonding without knowing whether or not it is an extraneous-c-p.

 

[Anydm]

"should" means something like "ought to be", doesn't it?

If the outdoor part of the water supply pipe were plastic (hence not an extraneous-c-p") it surely would not "ought to be bonded"? As was said, we can't tell whether it needs bonding without knowing whether or not it is an extraneous-c-p.

I appreciate your responses and agree that if the external part of the supply is plastic bonding would be unnecessary. I’m not sure how to establish this. Certainly the small section of pipe emerging from the solid floor is metallic (ie between the floor and the main stop-cock). At what point the supply pipe might change to plastic is anyone’s guess. What is the best way to ‘test’ this as suggested in your post. The only way I could think of would be a loop test between the short bit of pipe and earth rod with everything else disconnected?

 

[bernardgreen]

If the water supply pipe is metallic then it is an extraneous conductive part and in theory ( the regulations ) require it to be bonded to the main earth terminal. The main earth terminal is connected to the TT earth rod,

It is most likely the metallic water supply pipe has a larger surface area in contact with the Ground than the surface area of the main earth rod has in contact with the Ground.

Which could pose the question, Is (a) the water pipe bonded to the TT ground rod or (b) is the ground rod an extraneous conductive part bonded to the far lower impedance of the water supply pipe ?

 

[flameport]

combi boiler located in a room on the first floor does have all incoming and outgoing copper pipe work cross-bonded (although I didn’t think this was any longer necessary).

Not necessary today, and never was at any time in the past.

 

[CBW]

Can you post a photo of the stopcock arrangement?

 

[Anydm]

Can you post a photo of the stopcock arrangement?

I can but it won’t be until tomorrow. Thanks.

 

[davelx]

Not necessary today, and never was at any time in the past.

Yes, but have you ever been able to convince as Gas Safe engineer of that? I haven't, they just insist that they have been told it must be done, even when all the pipes are linked by a conductive manifold attached to the boiler mounting bracket. If you have, how?

 

[Anydm]

I can but it won’t be until tomorrow. Thanks.

Well I’m an idiot! When I came to look closer the incoming water pipe is indeed plastic. I had been distracted by the short length of copper between the adapter fitting and the stopcock. Pays to look closer before firing off queries on the forum! Thanks for all your input and apologies for inconvenience.

 

[CBW]

Well I’m an idiot! When I came to look closer the incoming water pipe is indeed plastic. I had been distracted by the short length of copper between the adapter fitting and the stopcock. Pays to look closer before firing off queries on the forum! Thanks for all your input and apologies for inconvenience.

No worries, at least you have your answer